William has taken 5 tests and his average score so far is 79. If he gets 100, a perfect score, on the remaining 2 tests, what will his new average be?
If he gets 100 on the remaining tests, the sum of his scores will be $5 \cdot 79 + 2 \cdot 100 = 595$ His overall average will then be $595 \div 7 = 85$.